#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	int number;
	int sum = 0;
	int count = 0;

	scanf_s("%d",&number,sizeof(number));
	while (number != -1) {
		sum += number;
		count++;
		scanf("%d,&number");

	}
	printf("%f\n", 1.0 * sum/count);
	return 0;
}